A cement composition has been used widely for external wall materials of buildings and structural bodies of construction since it can provide a cement hardened product excellent in strength and durability. Examples of such a cement composition include a cement paste prepared by adding water to cement, a mortar prepared by admixing sand, which is a fine aggregate, therewith, and a concrete prepared by further admixing gravel, which is a coarse aggregate, therewith. In general, in order to improve the air entrainment and fluidity, cement admixtures are added. Recently, their importance tends to be highly regarded and technical innovations have been developed for them.
The functions of the cement admixtures are to assure sufficient dispersing ability for the cement composition even if water content is decreased, retain the fluidity and workability of the cement composition, and improve the durability and strength along with decrease of water as well as to give an excellent cement composition with stable dispersing ability with the lapse of time. In concrete industrial fields today, concrete provided with such functions has been desired. In order to satisfy such requirements, it becomes very important to decrease the unit water quantity and, also, to prevent the decrease of the fluidity.
Among various cement admixtures, especially polycarboxylic acid type cement dispersants are advantageous as compared with other cement dispersants such as naphthalene ones in terms of excellent dispersing property. With respect to such cement dispersants, Japanese Kokai Publication Sho-57-118058 and Hei-09-142905 disclose cement dispersants comprising copolymers prepared by using predetermined unsaturated polyalkylene glycol ether monomers and maleic acid monomers at predetermined ratios, and Japanese Kokai Publication Sho-63-285140 discloses cement dispersants mainly comprising copolymers of polyoxyalkylene-monoalkenylalkyl ethers and maleic anhydride.
With respect to cement admixtures essentially comprising polycarboxylic acid copolymers and other components, Japanese Kokai Publication Hei-05-213651 discloses cement additives comprising copolymers of methoxypolyethylene glycol allyl ether and maleic anhydride and nitrous acid salts, and Japanese Kokai Publications Hei-09-241055 and Hei-09-286651 disclose use of polycarboxylic acid type cement dispersants with setting accelerators and setting retarders in combination. In addition, Japanese Kokai Publications Hei-05-43288 and 2002-187756 disclose use of polycarboxylic acid type cement dispersants with sulfonic acid type dispersants in combination.
However, these techniques do not completely solve decrease of fluidity with the lapse of time, namely “slump loss”, and there was a room for contrivance to improve the workability of a cement composition in undertaking construction by giving sufficient fluidity to the cement composition. Further, in a high water reducing ratio range required for high strength concrete, the fluidity of the concrete is deteriorated and, especially, the viscosity is increased under high share condition, so that the pump load becomes extremely high at the time of pump transportation and it becomes difficult to carry out pump transportation. Therefore, there was a room for contrivance in order to decrease the viscosity of the concrete composition, and improve the workability.
In particular, in the case of applying a cement composition under high temperature environments in summer or the like, it is desired to improve the workability and efficiently executing the cement composition by preventing decrease of fluidity of the cement composition and, simultaneously, sufficiently exhibit the functions of the cement hardened product. In the case of execution and hardening the cement composition at a low temperature environment, there was a room for contrivance to carry out cement composition applying and hardening work efficiently and obtain sufficient functions of the cement hardened product by providing high dispersing ability and slump loss preventing ability even in a high water reducing ratio range and, also, by giving the viscosity decreasing ability and shortening the hardening time and subsequently improving the workability.
On the other hand, with respect to polycarboxylic acid type cement dispersants, which are excellent in dispersing ability, since the addition amount necessary to obtain sufficient fluidity is low in a low water reducing ratio range, in the case the bland or the lot No. (manufacturing plants and manufacturing date) of cement is changed, the fluidity of the obtained concrete is changed even if the addition ratio of the dispersant to cement is same; therefore, there was a room for contrivance to obtain stable dispersing ability in terms of quality control. Further, with respect to mass concrete such as concrete for dams, from a viewpoint of prevention of cracking attributed to hydration heat and budget of the construction, the unit cement quantity is to be suppressed to 300 kg/m3 or less in some cases. In such a poor concrete, even if a polycarboxylic acid type cement dispersant excellent in the dispersing ability is used, water bleeding and separation of gravel tend to easily take place; therefore, there was a room for contrivance to improve the workability of the concrete composition.
Further, European Patent Publication No. 1179517 discloses cement dispersants comprising a copolymer, as an essential component, including constitutional unit derived from unsaturated (poly)alkylene glycol ether monomer and constitutional unit derived from (meth) acrylic acid (salt), and WO 02/096823 discloses cement admixtures comprising two polymers as essential constituents, namely a polymer (A1) comprising a constituent unit derived from an unsaturated (poly)alkylene glycol ether monomer and a constituent unit derived from an unsaturated monocarboxylic acid monomer, and a polymer (B1) containing an oxyalkylene group or polyoxyalkylene group and carboxyl group. These cement dispersants are capable of exhibiting high dispersing ability even in a slight amount of addition. However, together with the excellent dispersing ability and slump loss preventing ability even in a high water reducing ratio range, there was a room for contrivance to exhibit sufficient viscosity decreasing ability, and to improve the workability in executing cement composition.